Weights and Aerobics Firm Up Diabetes Control

CALGARY, Alberta, Sept. 18 -- Exercise strengthens glycemic control for type 2 diabetes patients whether they walk on a treadmill or pump iron, but combining aerobic and resistance exercise appears to have the greatest benefit.
In just six months, aerobic exercise reduced glycosylated hemoglobin A1c (HbA1c) levels by 0.43 percentage points and resistance training with weights reduced levels by 0.30 percentage points, reported Ronald J. Sigal, M.D., M.P.H., of the University of Calgary and colleagues in the Sept. 18 issue of Annals of Internal Medicine.
Although these groups improved significantly compared with sedentary controls (P=0.007 and P=0.038), patients who did both aerobic and resistance regimens more than doubled the benefit with a drop in HbA1c of 0.9 percentage points.
Other studies have shown that a similar 1% absolute decrease in HbA1c reduces major cardiovascular events 15% to 20% and microvascular complications of diabetes 37%, Dr. Sigal and colleagues added.
The findings affirm exercise as "probably the best strategy for modulating the mean glucose level," commented William E. Kraus, M.D., of Duke University, and Benjamin D. Levine, M.D., of the University of Texas Southwestern Medical Center in Dallas, in their accompanying editorial.
The results "should stimulate all clinicians to include exercise assessment and counseling into every clinic visit," they added.
Exercise has been well established as important to diabetes treatment, but many issues remain around the best "dose" and type of physical activity for patients.
As a "first pass" at addressing these issues, the researchers randomized 251 sedentary, type 2 diabetes patients ages 39 to 70 to one of three exercise regimens or a waiting list, which served as a control.
The regimens consisted of three 45-minute sessions a week of trainer-supervised exercise -- aerobic exercise on a stationary bicycle or a treadmill, resistance exercise on weight machines -- or a total of six sessions a week for the group assigned to both aerobic and resistance exercise.
Participants were given a weight-maintenance diet and weight loss was low in all groups (0.3 to 2.6 kg).
After a four week run-in period and 22 weeks on the study, the primary endpoint findings included:
A 0.51 percentage point HbA1c reduction in the aerobic exercise group versus controls (P=0.007).
A 0.38 percentage point HbA1c reduction in the resistance training group compared with controls (P=0.038).
An additional 0.46 percentage point HbA1c reduction in the combined exercise group compared with aerobic training alone (P=0.014).
An additional 0.59 percentage point HbA1c reduction in the combined exercise group compared with resistance training alone (P=0.001).
The benefit of exercise was greatest among those with poor glycemic control at baseline (P<0.001 for those with HbA1c at or above 7.5% versus those below 7.5%).
The secondary endpoints of blood pressure and lipid changes showed no significant changes, which might be accounted for by the high average body mass index (about 35 kg/m2) and relatively low exercise intensity that maintained the heart rate at 60% to 75% of maximal, Drs. Kraus and Levine noted.
However, the study was not designed to determine the effect of exercise intensity, duration, or volume, the researchers noted.
This made it unclear whether the extra benefit from combined exercise was because of the additional amount of time spent exercising or by altering glucose tolerance through complimentary mechanisms, Drs. Klaus and Levine cautioned. Further study may be needed to answer this question, they said.
Furthermore, the participants were "probably more adherent to exercise and healthier on average than the general population with type 2 diabetes," Dr. Sigal and colleagues said.
Also, the study excluded those receiving insulin or who had advanced diabetes complications and the findings may not be generalizable to unsupervised exercise programs, they added.
"Despite the study's limitations, a combined regimen of resistance and aerobic exercise is likely to be practical and safe," Drs. Kraus and Levine said. Adverse events and nonadherence were no greater in the combined exercise group than in either of the other exercise groups.
Regardless of which type of exercise is chosen, though, "in the shadow of a growing diabetes and obesity epidemic, failing to prescribe exercise to patients with diabetes is simply unacceptable practice," they concluded.
The DARE trial was supported by grants from the Canadian Institutes of Health Research and the Canadian Diabetes Association.
Dr. Sigal was supported by the Canadian Institutes of Health Research and the Ottawa Health Research Institute. The editorialists reported no conflicts of interest. Primary source: Annals of Internal MedicineSource reference: Sigal RJ, et al "Effects of Aerobic Training, Resistance Training, or Both on Glycemic Control in Type 2 Diabetes: A Randomized Trial" Ann Intern Med 2007;147:357-369. Additional source: Annals of Internal MedicineSource reference: Kraus WE, Levine BD "Exercise Training for Diabetes: The 'Strength' of the Evidence" Ann Intern Med 2007;147:423-424.